To critics, the few dozen researchers who met this week for a Washington conference are part of an ideological crusade, a modern-day sham meant to infect science with religious belief.

To participants, they are studying what they say is becoming increasingly obvious: the link between a person's religion or spirituality and their health.

The meeting Wednesday at the Reagan Building represented the growth of a research field that has existed on a small scale for decades but has expanded significantly in the past few years. The researchers include psychologists, sociologists, philosophers, statisticians and others who believe being religious or spiritual has health benefits.

While the field remains tiny -- about $5 million is spent worldwide on such research, experts estimate -- both sides view the stakes as huge.

Jennifer Marshall of the Heritage Foundation, one of the conference hosts, said the advocates' goal is to make religiosity one of the benchmarks that policymakers use to measure health, alongside other factors such as socioeconomic status and age.

But to the field's many challengers, empirical proof linking religiosity and health is weak. If being a church member improves one's health, it could be due to the social contact, and being on a soccer team could create the same results, they say. If prayer calms the heart, secular yoga class could as well.

These critics also say it is ethically dangerous for physicians to ask personal questions about faith because it could lead to evangelizing.

Still, the field is growing. Harold Koenig, a psychiatrist and behavioral scientist at Duke University, tallied about 6,200 published studies on the issue in professional journals before 2000, and 7,145 articles between 2000 and 2008.

Funding, however, doesn't appear to be increasing significantly. The federal government invested in recent studies that produced conflicting results. But interest from the John Templeton Foundation has been a massive boost, Koenig said, adding that it funds about 75 percent of today's research.

The field is working to become more credible, and to overcome early, well-publicized studies that looked at whether people's health would be improved if others prayed for them without their knowledge. Most mainstream scientists dismissed the research and even supporters of the field said the studies were not well done.

About half of U.S. medical schools now have courses on religion's link to health, said Byron Johnson, a Baylor University sociologist.

Columbia University behavioral psychiatrist Richard Sloan, a well-known critic of the research who was not at the conference, said the subject seems to be gaining ground because spirituality and health are booming American trends.

"The confluence of the two is irresistible to the media, and in general," he said. Policymakers are also looking at it more seriously, he said, "for no good reason. Understandable reasons, but none very good."

But measuring religiosity, and how to isolate it from other personal factors, is not possible, he said.

That, in fact, is something the researchers at the conference said they have struggled with.

Measuring how often someone attends worship services or prays cannot fully gauge an individual's beliefs. Such measurements also don't capture religion as it is practiced and understood in 2008, with many people moving away from denominational identity and church membership. Instead, conference participants discussed other yardsticks, such as people's perceptions of God, how close they feel to God, and how often they feel supported by their faith community.

Even within the field, there is a fissure over what exactly is being measured. Some are concerned that society looks more positively on "spirituality" -- feeling peaceful and connected with a higher power without rules, credo or community obligations -- while "religion" is seen as oppressive and judgmental, although easier to measure by worship attendance, tithing and frequency of Bible study.